This invention is generally directed to imaging members, and more specifically to oxytitanium phthalocyanines and processes for the preparation thereof. Specifically, the present invention is directed to simple, economical processes for obtaining the Type IV polymorph of oxytitanium phthalocyanine from dichlorotitanium phthalocyanine and layered photoconductive members comprised of the aforementioned Type IV polymorph of oxytitanium phthalocyanine. In one embodiment, the process of the present invention comprises the mixing, or formation of a slurry of a dihalotitanium phthalocyanine, such as dichlorotitanium phthalocyanine, in a mixture comprised of a trihaloacetic acid and an alkylene halide; thereafter adding the resulting slurry to an aqueous aliphatic alcohol mixture to enable hydrolysis of the dihalotitanium phthalocyanine to Type X oxytitanium phthalocyanine; separating the Type X oxytitanium phthalocyanine therefrom; and converting the Type X oxytitanium phthalocyanine obtained to Type IV oxytitanium phthalocyanine by the slurrying thereof with a halobenzene, such as chlorobenzene. Layered imaging members containing the Type IV oxytitanium phthalocyanine obtained by the processes of the present invention possess a number of advantages, such as high photoconductivity, low dark decay and excellent stability in xerographic cycling, for example from about 1 percent to about 20 percent cycle down after 50,000 imaging cycles. In an embodiment, the process of the present invention comprises the preparation of the Type IV oxytitanium phthalocyanine by the hydrolysis of dichlorotitanium phthalocyanine, preferably purified by slurrying in a solvent like dimethylformamide; the hydrolysis being accomplished by adding a slurry of the aforementioned dichlorotitanium phthalocyanine in trifluoroacetic acid and methylene chloride to a mixture comprised of methanol and water, and separating the Type X oxytitanium phthalocyanine therefrom by, for example, filtration. The obtained Type X oxytitanium phthalocyanine is converted to the desired Type IV by slurrying in chlorobenzene. The Type IV oxytitanium phthalocyanine obtained can be selected as an organic photogenerator pigment for use in photoresponsive imaging members containing charge, especially hole transport, layers comprised of aryl amine hole transport molecules. The aforementioned photoresponsive imaging members can be negatively charged when the photogenerating layer is situated between the hole transport layer and the substrate, or positively charged when the hole transport layer is situated between the photogenerating layer and the supporting substrate. The layered photoconductor imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible with toner compositions of the appropriate charge. Generally, the imaging members are sensitive in the wavelength regions of from about 700 to about 850 nanometers, thus diode lasers can be selected as the light source.
Many processes for the preparation of oxytitanium phthalocyanines are known, such as the sulfuric acid pasting methods, reference for example EPO publication 314,100. In the aforementioned Mita EPO Patent Publication 314,100, there is illustrated the synthesis of oxytitanium phthalocyanine, see for example pages 5 and 6, by, for example, the reaction of titanium alkoxides and diiminoisoindolene in quinoline or an alkylbenzene, and the subsequent conversion thereof to an alpha type pigment (Type II polymorph) by an acid pasting process, whereby the synthesized pigment is dissolved in concentrated sulfuric acid, and the resultant solution is poured onto ice to precipitate the alpha form, which is filtered and washed with methylene chloride. This pigment, which was blended with varying amounts of metal free phthalocyanine, could be selected as the electric charge generating layer in layered photoresponsive imaging members.
In Japanese 62-256865 there is disclosed, for example, a process for the preparation of pure Type I oxytitanium phthalocyanine involving the addition of titanium tetrachloride to a solution of phthalonitrile in an organic solvent which has been heated in advance to a temperature of from 160.degree. to 300.degree. C. In Japanese 62-256866, there is illustrated, for example, a method of preparing the aforementioned polymorph which involves the rapid heating of a mixture of phthalonitrile and titanium tetrachloride in an organic solvent at a temperature of from 100.degree. to 170.degree. C. over a time period which does not exceed one hour. In Japanese 62-256867, there is described, for example, a process for the preparation of pure Type II (alpha polymorph) oxytitanium phthalocyanine, which involves a similar method to the latter except that the time to heat the mixture at from 100.degree. to 170.degree. C., is maintained for at least two and one half hours. Types I and II, in the pure form obtained by the processes of the above publications, apparently afforded layered photoresponsive imaging members with excellent electrophotographic characteristics. Also, as mentioned in the textbook Phthalocyanine Compounds by Moser and Thomas, the disclosure of which is totally incorporated herein by reference, polymorphism or the ability to form distinct solid state forms is well known in phthalocyanines. For example, metal-free phthalocyanine is known to exist in at least 5 forms designated as alpha, beta, pi, X and tau. Copper phthalocyanine crystal forms known as alpha, beta, gamma, delta, epsilon and pi are also described. These different polymorphic forms are usually distinguishable on the basis of differences in the solid state properties of the materials which can be determined by measurements, such as differential scanning calorimetry, infrared spectroscopy, ultraviolet-visible-near infrared spectroscopy, and especially X-ray powder diffraction (XRPD) techniques. There appears to be general agreement on the nomenclature used to designate specific polymorphs of commonly used pigments such as metalfree and copper phthalocyanine. However, this does not appear to be the situation with oxytitanium phthalocyanines as different nomenclature is selected in a number of instances. For example, reference is made to alpha, beta, A, B, C, y, and m forms of oxytitanium phthalocyanine with different names being used for the same form in some situations. Five distinct crystal forms oxytitanium phthalocyanines are Types X, I, II, III, and IV.
In Sanyo-Shikiso Japanese 63-20365/86, reference is made to the known crystal forms alpha and beta oxytitanium phthalocyanines (Types II and I, respectively, it is believed), which publication also describes a process for the preparation of a new form of oxytitanium phthalocyanine. This publication appears to suggest the use of the unnamed oxytitanium phthalocyanine as a pigment and its use as a recording medium for optical discs. This apparently new form was prepared by treating acid pasted oxytitanium phthalocyanine (Type II form, it is believed) with a mixture of chlorobenzene and water at about 50.degree. C.
In U.S. Pat. No. 4,728,592, there is illustrated, for example, the use of alpha type oxytitanium phthalocyanine (Type II) in an electrophotographic device having sensitivity over a broad wavelength range of from 500 to 900 nanometers. This form was prepared by the treatment of dichlorotitanium phthalocyanine with concentrated aqueous ammonia and pyridine at reflux for 1 hour. Also described in the aforementioned patent is a beta type oxytitanium phthalocyanine (Type I) pigment, which is believed to provide a much poorer quality photoreceptor.
In Konica Japanese 64-17066/89, there is disclosed, for example, the use of a new crystal modification of oxytitanium phthalocyanine prepared from alpha type pigment (Type II) by milling it in a sand mill with salt and polyethylene glycol. This pigment apparently had a strong XRPD peak at a value of 2 theta of 27.3 degrees. This publication also discloses that this new form differs from alpha type pigment (Type II) in its light absorption and shows a maximum absorbance at 817 nanometers compared to alpha type, which has a maximum at 830 nanometers. The aforementioned Konica publication also discloses the use of this new form of oxytitanium phthalocyanine in a layered electrophotographic device having high sensitivity to near infrared light of 780 nanometers. The new form is indicated to be superior in this application to alpha type oxytitanium phthalocyanine (Type II). Further, this new form is also described in U.S. Pat. No. 4,898,799 and in a paper presented at the Annual Conference of Japan Hardcopy in July 1989. In this paper, this same new form is referred to as Type Y, and reference is also made to Types I, II, and III as A, B, and C, respectively.
Processes for the preparation of specific polymorphs of oxytitanium phthalocyanine, which require the use of a strong acid such as sulfuric acid, are known, and these processes, it is believed, are not easily scalable for manufacturing purposes and generally lead to some decomposition of the organic pigment. One process as illustrated in Konica Japanese Laid Open on Jan. 20, 1989 as 64-17066 (U.S. Pat. No. 4,643,770 appears to be its equivalent), the disclosure of which is totally incorporated herein by reference, involves, for example, the reaction of titanium tetrachloride and phthalonitrile in 1-chloronaphthalene solvent to produce dichlorotitanium phthalocyanine which is then subjected to hydrolysis by ammonia water to enable the formation of the Type II polymorph. This phthalocyanine is preferably treated with an electron releasing solvent such as 2-ethoxyethanol, dioxane, or N-methylpyrrolidone, followed by subjecting the alpha oxytitanium phthalocyanine to milling at a temperature of from 50.degree. to 180.degree. C. In a second method described in the aforementioned Japanese Publication, there is disclosed the preparation of alpha type oxytitanium phthalocyanine with sulfuric acid. A method for the preparation of Type IV oxytitanium phthalocyanine involves the addition of an aromatic hydrocarbon, such as chlorobenzene solvent, to an aqueous suspension of an oxytitanium phthalocyanine prepared by the well known acid pasting process, and heating the resultant suspension to about 50.degree. C. as disclosed in Sanyo-Shikiso Japanese 63-20365, Laid Open in Jan. 28, 1988. In Japanese 171771/1986, Laid Open Aug. 2, 1986, there is disclosed the purification of metal phthalocyanines by treatment with N-methylpyrrolidone.
To obtain an oxytitanium phthalocyanine based photoreceptor having high sensitivity to near infrared light and especially to provide a photoreceptor which can be repeatedly cycled in the xerographic process, it is believed necessary to control not only the purity and chemical structure of the pigment, as is generally the situation with organic photoconductors, but also to prepare the pigment in the correct crystal form. The disclosed processes used to prepare specific crystal forms of oxytitanium phthalocyanine are either complicated and difficult to control as in the preparation of pure Types I and II pigment by careful control of the synthesis parameters by the processes described in Mitsubishi Japanese 62-25685, -6 and -7, or involve harsh treatment such as sand milling at high temperature, reference Konica U.S. Pat. No. 4,898,799; or dissolution of the pigment in a large volume of concentrated sulfuric acid, a solvent which is known to cause decomposition of metal phthalocyanines by sulfonation or demetallization, reference Sanyo-Shikiso Japanese 63-20365 and Mita EPO 314,100.
Generally, layered photoresponsive imaging members are described in a number of U.S. patents, such as U.S. Pat. No. 4,265,900, the disclosure of which is totally incorporated herein by reference, wherein there is illustrated an imaging member comprised of a photogenerating layer, and an aryl amine hole transport layer. Examples of photogenerating layer components include trigonal selenium, metal phthalocyanines, oxymetallo phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006 a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in the '006 patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles.
In a copending application U.S. Ser. No. 537,714, the disclosure of which is totally incorporated herein by reference, there are illustrated photoresponsive imaging members with photogenerating oxytitanium phthalocyanine layers prepared by vacuum deposition. It is indicated in this copending application that the imaging members comprised of the vacuum deposited oxytitanium phthalocyanines and aryl amine hole transporting compounds exhibit superior xerographic performance, since low dark decay characteristics result and higher photosensitivity is observed, particularly in comparison to several prior art imaging members prepared by solution coating or spray coating, reference, for example, U.S. Pat. No. 4,429,029 mentioned herein.
In U.S. Pat. No. 5,153,313, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of phthalocyanine composites which comprises adding a metal free phthalocyanine, a metal phthalocyanine, an oxymetallo phthalocyanine or mixtures thereof to a solution of trifluoroacetic acid and a monohaloalkane; adding to the resulting mixture an oxytitanium phthalocyanine; adding the resulting solution to a mixture that will enable precipitation of said composite; and recovering the phthalocyanine composite precipitated product.
In U.S. Pat. No. 5,200,359 there is disclosed a process for the preparation of oxytitanium phthalocyanine which comprises the treatment of Type X oxytitanium phthalocyanine with a halobenzene; and more specifically, in one embodiment of this copending application there are provided processes for the preparation of Type X oxytitanium phthalocyanine which comprises the solubilization of a Type I oxytitanium phthalocyanine, which can be obtained by the reaction of 1,3-diiminoisoindoline and titanium tetrabutoxide in the presence of a solvent, such as chloronaphthalene, reference U.S. Pat. No. 5,189,156 the disclosure of which is totally incorporated herein by reference, in a mixture of trifluoroacetic acid and methylene chloride, precipitation of the desired Type X oxytitanium phthalocyanine, separation by, for example, filtration, and thereafter subjecting the product to washing with fluorobenzene; more specifically, U.S. Pat. No. 5,189,156 discloses a process for the preparation of oxytitanium phthalocyanine which comprises the reaction of a titanium tetraalkoxide and 1,3-diiminoisoindoline in the presence of a halonaphthalene solvent; dissolving the resulting Type I oxytitanium phthalocyanine in a haloacetic acid and an alkylene halide; adding the resulting mixture slowly to a cold alcohol solution; and thereafter isolating the resulting Type X oxytitanium phthalocyanine with an average volume particle size diameter of from about 0.02 to about 0.5 micron; and U.S. Pat. No. 5,189,155 discloses a process for the preparation of Type I oxytitanium phthalocyanine which comprises the reaction of titanium tetraalkoxide and 1,3-diiminoisoindoline in the presence of a halonaphthalene solvent. The product can be identified by various known means including X-ray powder diffraction (XRPD). Also, in U.S. Pat. No. 5,166,339 there is disclosed a process for the preparation of titanyl phthalocyanine which comprises dissolving a titanyl phthalocyanine in a solution of trifluoroacetic acid and methylene chloride; adding the resultant solution to a solvent system that will enable precipitation; and separating the desired titanyl phthalocyanine from the solution followed by an optional washing; U.S. Pat. No. 5,182,382 discloses a process for the preparation of titanyl phthalocyanine Type X which comprises dissolving titanyl phthalocyanine Type I in a solution of trifluoroacetic acid and methylene chloride; adding the resultant solution to a solvent enabling precipitation of Type X titanyl phthalocyanine; separating the titanyl phthalocyanine Type X from the solution; followed by a first washing with an organic solvent and a second washing with water; and thereafter a solvent treatment with fluorobenzene; and U.S. Pat. No. 5,164,493 discloses a process for the preparation of titanyl phthalocyanine which comprises the reaction in a solvent of phthalonitrile and diiminoisoindoline with titanium tetraalkoxide.
The disclosures of each of the aforementioned copending patent applications and patents are totally incorporated herein by reference.